The invention relates to infinitely variable traction roller transmissions in which motion is transmitted from a toric disc mounted on an input shaft to a toric disc mounted on an output shaft by traction rollers disposed between and in engagement with the toric discs.
To enable such toroidal traction roller transmissions to transmit large torques at high speeds for long life the traction rollers are positioned inwardly of the center of the toroidal cavity between the toric discs. Such an arrangement causes relatively little spin in the contact area of the traction rollers with the toric discs so that a relatively high traction coefficient and relatively little wear on the surfaces of the toric discs and the traction rollers are obtained. The contact forces necessary for engagement of the traction rollers with the toric discs are obtained by forcing the toric discs toward each other. This, however, results in a large axial thrust load of the traction rollers which is carried on to axial thrust bearings supported by the housing of the rotary motion transmitting device as shown for example in U.S. Pat. No. 3,299,744. In such arrangements, the housings do not only have to take up the bearing forces, but a large amount of vibrations is also carried from the traction rollers into the housings. Furthermore, the transmission ratio control arrangements for such devices include mechanical actuating means, which also carry noises and vibrations to the housing. The positioning controls for the rollers are usually interconnected thereby causing backlash, deflections and undampened movements that interfere with balanced operation.
In the present inventor's earlier U.S. Pat. No. 3,810,398 a rotary motion transmitting device is provided in which the support structures of the power rollers are interconnected by tension means which extend between the toric discs and balance the forces and vibrations exerted on the power rollers while allowing nearly friction free transverse motion of the roller assemblies for transverse shifting of the roller assembly for transmission ratio changing pivoting of the roller support structure. The traction roller positions are controlled independently so that very little noise and vibration is carried into the housing. However, under cold operating conditions the transmission fluid has a relatively high viscosity so that the forces engaging the traction rollers are not sufficient to squeeze out the transmission fluid film. As a result, hydroplaning may occur which may cause the power rollers to move out of their desired relative positions that is out of the same circles of contact with the toric discs.